A problem in the growth of layers of ternary or quaternary compositions by liquid phase epitaxy processes is to produce layers of a reproducible composition and thickness. This problem is particularly significant in processes using a sliding boat method due to the small quantity of liquid used for growing a layer, which makes composition control difficult, and also when growing ternary materials having a general formula X.sub.x Y.sub.1-x Z in which the solid deposited from a liquid solution has a very different X:Y ratio from that prevailing in the liquid. Many of the III-V compounds show this effect, as does cadmium mercury telluride. In a sliding boat method, a substrate is contacted with a solution of the layer material, which solution must at some stage of the contact time be supersaturated in order to allow growth to occur. Since for most solvents used in liquid phase epitaxy, the solubility of the layer material in the solvent increases with increasing temperature, it is possible to define a saturation temperature T.sub.s below which the solution is supersaturated with respect to the layer material.
It may be difficult to prepare a growth solution having a predetermined composition by weighing each of the constituents of the solution sufficiently accurately, particularly when one of these constituents forms a small proportion (say less than 5% by weight) of the solution, and it would be necessary in such a case to add this constituent in the form of very fine particles, thus having a large specific surface and being prone to contamination.
It is desirable in a manufacturing process of liquid phase epitaxy growth that each charge of solution used should have an almost identical T.sub.s value. Preferably each charge should consist of essentially the same quantity of material in order that both the composition and thickness of the grown epitaxial layers should be consistent.